In ophthalmic optics, lens blanks are formed from glass or plastic, and a convex or concave surface of the lens is mounted upon a retaining member known as a lens block. The lens and block are then accurately mounted upon a grinding apparatus wherein a toroidal surface of compound prescriptive value is "rough ground" into a concave portion of the lens. In this regard, a first principal meridian of the lens typically has a different dimension with respect to a second principal meridian normal to the first. Following the initial grinding operation, an ophthalmic lens is fined and then polished to a final prescriptive value. Left and right lenses are then mounted upon an edge grinding machine to cut the outer peripheral shape required for compatibility with an eyeglass frame of an ultimate user or wearer.
In its evolution, the toric lens fining and polishing field of technology has followed a path that had its roots in systems ranging from wheel systems to various oscillatory machines, such systems and machines being directed toward the objective of having a toric lens finished to a desired configuration. In most cases, such systems and machines did an adequate job. However, the processing time was lengthy.
In response to the inadequacies of such first-generation systems and machines, a second generation of systems and machines based on the concept of a gimbal-supported tool was introduced. By way of example, such a second-generation toric finer-polisher is disclosed in U.S. Pat. No. 3,732,647--Stith, assigned to Coburn Manufacturing Company, Inc. of Muskogee, Okla. Such second-generation arrangements allowed for faster movement of the fining-polishing mechanism, and therefore processing time was reduced.
The finer-polisher machine of the aforementioned U.S. patent was used to finish cylindrical lenses. In such cylindrical lens finishers, the toric surface of a lapping tool must be held in engagement with the lens surface and moved relative thereto in a path referred to as a "break-up" motion. Such break-up movement prevents ridges, grooves and other aberrations from being formed in the lens surface, such ridges, grooves and aberrations occurring when regular or uniform motion is utilized. In addition to orbital, break-up motion of the lapping tool, the aforementioned U.S. patent discloses movement of the lens in a transverse motion from side to side. In at least one other system, front to rear motion is added to the transverse motion of the lens to be finished.
Although finer-polisher systems of the type described in the aforementioned U.S. patent were widely utilized, room for significant improvement remained. For example, systems such as that disclosed in the aforementioned U.S. patent suffered from relatively low speed of motion between the lapping tool and the lens, and any attempt to increase the relative speed of motion between the lapping tool and lens caused a sacrifice in the lens finishing ability of the system. It was also considered desirable to be able to easily vary the amplitude of the orbital, break-up motion of such a system.
As a result of attempts to overcome the disadvantages of the system disclosed in the aforementioned U.S. patent of Stith, an improved finer-polisher machine was developed, and is disclosed in U.S. Pat. No. 4,320,599--Hill et al, which is also assigned to Coburn Manufacturing Company, Inc. of Muskogee, Okla. In the arrangement disclosed in this patent, first and second assemblies were provided for carrying a lapping tool and a lens, respectively, and for imparting an orbital break-up motion during the fining and polishing operation. The amplitude of orbital movement in this arrangement was variable by application of a cam assembly for adjustment of the degree of orbital break-up motion of the lens mounting and/or lapping tool. However, there was also a disadvantage with this system in that it was not possible to decrease the speed and amplitude of motion of a lens lapping tool for enhanced control, while at the same time maintaining the feet-per-minute of relative motion between a lens and the tool to facilitate rapid fining and polishing. It was also considered desirable to have a system for achieving motion in an X-Y plane which would eliminate any tendency for the creation of a sawtooth aberration in the lens. Elimination of these problems was thought to be desirable because the rate of finishing of an ophthalmic lens could be increased without sacrificing lens finishing quality of the system.
Accordingly, a further finer-polisher apparatus was developed, and is disclosed in U.S. Pat. No. 4,521,994--Tusinski, which is also assigned to Coburn Manufacturing Company, Inc. of Muskogee, Okla. The arrangement of the Tusinski patent provides for a frame and gimbal-mounted assembly for providing an orbital break-up motion to a lens lapping tool, in combination with an X-Y motion assembly connected to the frame and lens for providing a smooth, Lissajous figure movement to the lens. In the X-Y motion assembly, commonly driven first and second cams provide movements in the X and Y directions, respectively.
In general, in break-up motion devices used with cylindrical lens surfaces, the base and cross-curve of the lapping tool must be maintained in parallel relationship with respect to the base and cross-curve of the lens. The finer-polisher machines of the aforementioned patents employed a gimbal assembly suspended between a pair of brackets extending outwardly from the sidewall of the machine, the gimbal assembly being located a relatively short distance, as measured along a connector rod, from the top of the lapping tool. The gimbal prevents any rotation of the aforementioned rod about its own longitudinal axis, and this is important because the cylindrical surface of the lapping tool must be maintained in accurate rotational alignment with the surface of the lens to be ground. Moreover, the gimbal provides an intermediate point along the length of the rod for pivotally supporting the rod such that the combined rotational and orbital motion imposed on the rod and transmitted via the rod to the lapping tool is both accurate and proportional.
The short radius from the gimbal to the top of the tool has, however, posed problems. For example, lens hydroplaning and excessively long strokes of the tool have resulted. As a result of these deficiencies, complex break-up motions have been required, especially in order to cope with some of the idiosyncrasies of the machines. More and more complex break-up motions have tended to reduce some of the problems. However, such complex motions have had the disadvantage of adversely influencing the integrity of the lens surface radii, which in turn has degraded optical integrity. In some cases, rubber supports have been used in order to compensate for this problem by allowing the tool to move or rotate off-axis. However, this has created a serious flaw in axis integrity which, in some cases, has followed an "S" path instead of a straight line as desired.
Another problem with the X-Y motion assembly of the prior art, in particular that assembly disclosed in the aforementioned patent of Tusinski, involves the exposure of a sliding part of the assembly to abrasive materials created by the fining-polishing operation. Specifically, such X-Y assemblies of the prior art created Y-axis motion by mounting the rocker arm carrying the polishing pins on a rod, the rod being disposed inside of a cylinder so that sliding motion of the rod with respect to the cylinder produced the Y-axis motion of the polishing pins. However, as a result of this arrangement, the exterior surface of the sliding rod was exposed to abrasive materials created by the fining-polishing process, and such abrasive materials became lodged between the sliding rod and its encompassing cylinder, causing damage and/or inefficiency in operation to the X-Y motion assembly.
The following additional patents are considered to be of background interest relative to the present invention: U.S. Pat. No. 913,543--Nichols; U.S. Pat. No. 998,101--Laabs; U.S. Pat. No. 1,593,212 Hart; U.S. Pat. No. 2,051,329--Cook; U.S. Pat. No. 2,176,154--Shannon; U.S. Pat. No. 2,208,527--Houchin; U.S. Pat. No. 2,371,303--Liebowitz; U.S. Pat. No. 3,258,879 Edelstein; U.S. Pat. No. 3,330,075--Suddarth et al; U.S. Pat. No. 3,552,899--Tagnon; and French Pat. No. 755,354--Heim et al.